The humanPCPH proto-oncogene: cDNA identification, primary structure, chromosomal mapping, and expression in normal and tumor cells

ENTPD5: identification of splicing variants and their impact on cancer survival

NTPDase5 is a nucleotidase of the endoplasmic reticulum that plays an important role in proteostasis as a regulator of protein N-glycosylation. This enzyme was first identified in hamster as a proto-oncogene activated upon a single nucleotide deletion that causes a frameshift leading to a truncated protein. Truncated NTPDase5 proteins were detected in human samples, but an oncogene was never identified. Searching for transcript variants in the GenBank database and using TCGA data, we discovered that splice variants could originate truncated human NTPDase5 proteins. We identified three main splicing events in the ENTPD5 gene: alternative acceptors, exon skipping, and alternative terminators. The analysis of impact of splicing events in cancers showed that skipping of exon 11-the event that leads to truncated proteins similar in size to the hamster oncogene-does not affect the hazard ratio of most tumors and was, in fact, a protective factor in the only two cancer studies where it was significant. We also identified four main patterns of impact of ENTPD5 in cancer and a potential variant-specific regulation by miR-215. Our findings shed light on a two-decade uncertainty about the origin of truncated NTPDase5 and contribute to the characterization of its impacts in cancer.

Distribution of NTPDase5 and NTPDase6 and the regulation of P2Y receptor signalling in the rat cochlea

Membrane-bound ectonucleoside triphosphate diphosphohydrolases (E-NTPDases) in the inner ear regulate complex extracellular purinergic type-2 (P2) receptor signalling pathways through hydrolysis of extracellular nucleoside 5'-triphosphates and diphosphates. This study investigated the distribution of NTPDase5 and NTPDase6, two intracellular members of the E-NTPDase family, and linked this to regulation of P2 receptor signalling in the adult rat cochlea. These extracellular ectonucleotidases preferentially hydrolyse nucleoside 5'-diphosphates such as UDP and GDP. Expression of both enzymes at mRNA and protein level was detected in cochlear tissues and there was in vivo release of soluble NTPDase5 and 6 into cochlear fluids. Strong NTPDase5 immunostaining was found in the spiral ganglion neurones and supporting Deiters' cells of the organ of Corti, while NTPDase6 was confined to the inner hair cells. Upregulation of NTPDase5 after exposure to loud sound indicates a dynamic role for NTPDase5 in cochlear response to stress, whereas NTPDase6 may have more limited extracellular roles. Noise-induced upregulation of co-localised UDP-preferring P2Y(6) receptors in the spiral ganglion neurons further supports the involvement of NTPDase5 in regulation of P2Y receptor signalling. Noise stress also induced P2Y(14) (UDP- and UDP-glucose preferring) receptor expression in the root processes of the outer sulcus cells, but this was not associated with localization of the E-NTPDases.

Gradual deregulation and loss of PCPH expression in the progression of human laryngeal neoplasia

PCPH is a gene involved in the regulation of eukaryotic cell proliferation and stress response. Recently, analyses of human and animal solid tumors and cell lines suggested that PCPH protein deregulation may participate in neoplastic progression. To test this possibility, we first examined PCPH expression in several laryngeal carcinoma cell lines by Western analysis. The results showed the presence of altered PCPH polypeptides in these cells, accompanied by the loss of the PCPH form present in normal laryngeal epithelial cells, a deregulated expression pattern similar to that reported previously. We then analyzed PCPH expression in 59 dysplastic lesions of the human larynx, representative of the mild, moderate, and severe stages of the disease. Immunohistochemical data showed that, compared with normal laryngeal mucosa, PCPH expression in the dysplastic samples was associated with areas of epithelial cell maturation rather than with regions of increased proliferation. Furthermore, PCPH expression decreased parallel to the increase in cellular atypia of the dysplastic samples: PCPH either was expressed at very low levels or not expressed in cases of severe dysplasia/carcinoma in situ. This trend toward loss of PCPH expression along malignant progression of the larynx was confirmed by the low to null expression of PCPH in samples of invasive laryngeal carcinoma and by the complete absence of PCPH immunostaining in a laryngeal carcinoma-derived liver metastasis. These results indicated that PCPH protein analysis might allow for the distinction between grades of laryngeal dysplasia. In addition, detection of altered PCPH polypeptides by Western analysis potentially can be applied to the early identification of laryngeal squamous cell carcinoma.

Deregulated expression of the PCPH proto-oncogene in rat mammary tumors induced with 7,12-dimethylbenz[a]anthracene

The PCPH proto-oncogene was identified by its frequent activation in Syrian hamster fetal cells exposed to 3-methylcholanthrene. We previously isolated human PCPH cDNA and studied its expression in normal human tissues. We report herein the pattern of PCPH expression in normal rat tissues. Each tissue expressed one major PCPH polypeptide that varied in molecular mass in different tissues. Normal mammary gland expressed a single PCPH polypeptide of 27 kDa. This PCPH form also was expressed in lactating mammary glands but at significantly greater levels. These results suggest the existence of tissue-specific regulatory mechanisms for PCPH expression that may be influenced by the differentiation stage. Our previous studies on the involvement of PCPH in human cancer showed that human breast tumor cell lines have frequent alterations in PCPH, including multiple PCPH polypeptide forms that are not expressed in normal cells. These cell lines also have frequent loss of a 27-kDa form identified as the only PCPH polypeptide expressed by normal human breast epithelial cells. In this study, we found that these same alterations occurred in vivo during mammary carcinogenesis in Sprague-Dawley rats treated with 7,12-dimethylbenz[a]anthracene, in both benign and malignant tumors, indicating that stable changes in PCPH expression took place early in the neoplastic process. Results showed that this experimental system is relevant to human breast carcinogenesis and provides an excellent model to study the molecular basis of the regulation of PCPH expression during normal differentiation and pathologic stages of neoplasia of the mammary gland and to analyze the role of PCPH in the carcinogenic process. Furthermore, the detection of atypical PCPH polypeptides in tumors suggests that PCPH immunodetection may be applied as a diagnostic tool for the early identification of neoplastic breast epithelial cells.

Expression of the protein product of the PCPH proto-oncogene in human tumor cell lines

Expression of the Protein Product of the PCPH Proto-oncogene in Human Tumor Cell Lines. Exposure of Syrian hamster embryo fibroblasts to chemical carcinogens resulted in the oncogenic activation of the PCPH proto-oncogene by induction of a single base-pair deletion that generated a truncated PCPH oncoprotein (mutated PCPH). Recently, we isolated and characterized the cDNA for the human PCPH proto-oncogene and determined that in humans PCPH is a single-copy gene located in chromosome 14 (14q24.3). Pilot mRNA expression studies indicated that PCPH was expressed in the majority of normal organs tested, particularly in liver and kidney, but it appeared to be expressed either at low levels or not at all in tumor cells or cell lines derived from the high-expressing tissues. We have generated an antiserum against bacterial recombinant Syrian hamster PCPH. This antiserum recognizes both the normal and truncated, oncogenic Syrian hamster PCPH proteins and cross-reacts with the yeast, mouse, rat and human homologue proteins. Using this antibody, we have performed a study of PCPH expression in a larger sample of human neoplastic cell lines, including some derived from breast, nervous system, colon, lung and pancreas tumors. Results confirmed the frequent lack of PCPH expression in malignant cells and identified several immunoreactive forms of PCPH being differentially expressed in cells of diverse tissue origins.